The Antiproton Source: A rich history and an exciting future

This is a mock-up of the proposed upgrades to the Antiproton Source and the new Mu2e building.

Fermilab's Antiproton Source has long produced the antimatter that makes Fermilab's particle collisions possible. While the Antiproton Source will shut down along with the Tevatron on Sept. 30, there are plans for its future.

The facility that houses the Antiproton Source will be reconfigured for two proposed experiments: Muon g-2 and Mu2e. Instead of creating antiprotons, both experiments will use the reconfigured facility to generate intense muon beams. While each would produce exciting and interesting data, they are both very different from the Antiproton Source's original mission.

Fermilab's Antiproton Source came out of an upgraded design of a similar machine that was housed at CERN.

Fermilab's first antiprotons were produced in the Tevatron's first collider run in 1988. At that time, it took more than an hour to make 1010 antiprotons. Now, the Antiproton Source can make 30x1010 antiprotons an hour.

"The antiproton production rate in those early days now seems like an incredibly slow pace," said Steve Werkema, deputy head of the Antiproton Source. "I think we would've been amazed by the production number now."

The Antiproton Source was upgraded in the mid-1990s, before collider Run II. Improved accelerator optics and upgraded stochastic cooling systems aided in the jump of antiproton production. The rate of antiprotons produced jumped significantly during this time, due to the combined efforts of improved accelerator complex components.

"We really have to recognizethe efforts by the operators," Werkema said. "There are long periods of routine running, and the operators are not happy to merely sit and watch the beam. They get to work tuning the machine. I think a good part of the improvements are due to the amazing things they've done."

More than tuning is necessary to convert the Antiproton Source facility into an area appropriately equipped to house the Muon g-2 and Mu2e experiments. Fermilab's muon program is a strong component of the laboratory's new direction. The laboratory will use muon beams to study fundamental laws of physics. Both of these experiments are possible, in large part, because of the cost savings that comes from reusing the Antiproton Source infrastructure.

These muon experiments will be at the cutting-edge of high-energy physics for Fermilab's push into the Intensity Frontier in the coming decade. Both experiments are currently in their design stage, with scientists and engineers finalizing conceptual designs. Muon g-2, the smaller of the two experiments, is aiming to start construction in 2013 and begin taking data in early 2016. Mu2e expects to finalize their conceptual design this year and is working toward a construction period that would allow for data production toward the end of the decade.

"There's a lot of work to do moving forward," Werkema said. "We're sad to see the Antiproton Source go, but we're going to be busy."

Muon g-2 is the newest generation of a similar experiment performed at Brookhaven National Laboratory in 2001, which found a disagreement in the data value and the Standard Model prediction of the gyromagnetic ratio "g" of the muon.

"We're doing the same type of experiment, but with higher precision," said Chris Polly, project manager for Muon g-2. "The Antiproton Source infrastructure plays a key role in getting to that higher precision. By building a 1,000 meter long beam line at Fermilab, the muon beam will have a much higher quality than what could be achieved with the 80 meter beamline used at Brookhaven."

The Antiproton Source was not designed to employ the high beam intensities needed for these experiments. However, the scientists see a lot of potential in the current facility.

"The Antiproton Source rings makes Fermilab the ideal place to do the Mu2e experiment," said Bob Bernstein, the Mu2e co-spokesperson. "Their length happens to be just right for our physics needs."

The Mu2e experiment will increase the intensity of muons stopping in their target by four orders of magnitude over any prior experiment. The discovery potential and the techniques developed for Mu2e will pave the way for future possibilities with Project X, a proposed high-intensity proton accelerator that would generate high-intensity beams for various experiments.

"Working with regular matter seems like it would be boring after making antiprotons, but, thankfully, it's not," Werkema said. "Both of these experiments come with unique and serious challenges. We won't be bored."